Characterisation is something that develops with practice. The more you write the more you get a “feel” for characters; you feel like you could reach out and touch them, yet, early in your story, they are usually more like people you’ve only just met. You need to use clues to “read” them just as you would a new acquaintance. It’s these clues that you need to pass on to your reader, so that s/he can do the same. So it might help you to think, “If I were meeting this character, what would I notice about him or her?”